The present invention relates to thermoplastic polymer blends which can be molded into plastic articles having improved properties. The polyblends of the present invention contain graft copolymer of a vinyl halide or of a vinyl halide and a comonomer copolymerizable therewith on a polyolefin component. Such copolymers are hereinafter referred to as "vinyl halide-polyolefin graft copolymers". The blends described in the present invention also contain polycarbonate polymers.
Polyvinyl halide, especially polyvinyl chloride polymers are widely used thermoplastic materials having many favorable properties. Such conventional non-graft vinyl halide polymers do not have heat distortion temperatures which are sufficiently high to adapt such polymers to much more wide use. Moreover, such polymers, especially rigid polyvinyl halide polymers, do not have a high impact resistance at ambient or subambient temperatures. Thus, at ambient temperature, i.e., at about 20.degree. C., corresponding to about 68.degree. F., the noted Izod impact resistance of vinyl halide homo- and copolymers is only of the order of about 0.4 to less than about 1 ft-lb/inch. At subambient temperatures, e.g., down to -20.degree. F. or lower, the notched Izod impact resistance of these polymers becomes vanishingly small or negligible.
It has been previously proposed to add minor amounts of an appropriate polymer additive, or additives, to improve ambient impact resistance of conventional polyvinyl polymer compositions. Usually, such additives are useful in ranges from about 3 to about 15 percent by weight of the polyvinyl halide polymer. Among the materials which have been found acceptable as polyvinyl halide impact modifiers are ABS polymers. Such impact modifiers moderately enhance the ambient temperature impact resistance of conventional vinyl halide polymers, i.e., generally raise the ambient temperature notched izod impact resistance of the polymer to about 2 to 10 ft-lbs/inch. However, these impact modifiers are relatively ineffective in imparting a satisfactory subambient temperature impact resistance to the polymer, i.e., the -20.degree. F. notched Izod impact resistance of the polymer containing the impact modifier is well below 1 ft-lb/inch and usually is about 0.4 to 0.5 ft-lb/inch.
Recently, vinyl halide-polyolefin graft copolymers have been developed to be a commercial reality. Such copolymers are produced by polymerization of vinyl halide (or a monomer mixture of vinyl halide and copolymerizable ethylenically unsaturated comonomer) in the presence of a polyolefin elastomer. Such reaction yields a polymer product which contains vinyl halide polymer chains bound, i.e., grafted at various sites along the chain of the trunk olefin as well as ungrafted vinyl halide polymer and ungrafted polyolefin. The graft polymer product, especially the graft polymer product prepared by a liquid phase bulk polymerization reaction, has improved impact resistance at both ambient temperatures and subambient temperatures, compared to the aforementioned conventional, i.e., ungrafted, vinyl halide polymers, even when the latter are blended with a conventional polyvinyl halide impact modifying polymer additive.
The bulk polymerization-prepared graft polymer product is even distinguished from the corresponding graft polymer prepared by a non-bulk polymerization technique, e.g., suspension polymerization, by an enhanced impact resistance at both low and ambient temperature and by breakage by the desirable ductile breakage mode rather than by an undesirable brittle breakage mode.
U.S. Pat. Nos. 4,005,037, 4,105,711 and 4,239,861 describe the blends of polyvinyl chloride homopolymer with polycarbonate polymers. Even though the blends described in these patent applications have increased heat distortion temperatures, they suffer from a significant disadvantage in that the impact strengths of these blends are poor, making them unsuitable for a large number of applications where resistance to impact is desirable in a plastic component. The problem of poor impact strength at these blends worsens at subambient temperatures (-20.degree. F. or lower).
It has now been found that further improved polymer products can be prepared by blending the vinyl halide polyolefin graft polymers, especially those produced by a liquid phase bulk polymerization reaction and polycarbonate polymers described hereinafter.
The molecular miscibility exhibited by the matrix phases of these polymeric components of the invention offers several advantages. The miscibility provides excellent mechanical compatibility. Superior weld line strengths and improved surface properties can be obtained when the polymeric components exhibit molecular miscibility. A problem of possible deterioration of the properties due to phase separation during or after processing may exist for an immiscible blend. This is likely in case of the injection molding process which typically uses very high shear rates. This problem is unlikely in a case where the polymeric components exhibit molecular miscibility.